Presentation on theme: "Developing a generic approach for modelling production processes covered in BREW Morna Isaac, Martin Patel."— Presentation transcript:
Developing a generic approach for modelling production processes covered in BREW Morna Isaac, Martin Patel
The aim:Analysis of the manufacturing process of products for which only basic data are available Relevancy:Products in an early stage of development and/or with data limitations due to competitive sensitivity Methodology: Available data will be used to develop generic elements of processes. Focus: Energy use, as a first indication of environmental impact, and costs
The main stages of a process: 1. Feedstock treatment (activation): Depends mainly on the type of feedstock, not on the desired product 2. Biological conversion 3. Product separation 4. Waste treatment and utilities
Feedstock types and their treatment: FeedstockTreatmentEnergy consumption SugarExtraction of juice StarchEnzymatic saccharification Corn wet milling 3.718-5.631 MJ final /kg glucose 1 Lignocellulosic (woody) Pretreatment, hydrolysis and saccarification Corn stover: 1 kg steam/kg sugar + 0.25 MJe/kg sugar 2 Plant oil Pyrolysis oil ExtractionSoybean milling: 1.8 MJ fossil /kg oil 1 Gerngross, 1999 2 NREL, 2002. For comparison according to Lynd et al., 1996 for pretreatment of poplar feedstock: 0.69 kg steam/kg sugar + 0.55 MJe/kg sugar
Major energy uses, aerobic processes: ItemGeneral dataPHA fermentation (Gerngross, 1999) Sterilization steam Batch 0.2-0.4kg/l broth, continuous up to 75% less 1 0.45 kg steam/kg PHA Aeration0.5-2.0 vvm, for 1.0 vvm: 5 kW/m 3 1 4.57 MJe/kg PHA Agitation1-3 kW/m 3 broth 1 1.15 MJe/kg PHA CoolingHeat produced: 15.7 MJ/kg-O 2 consumed 2 2.74 MJe/kg PHA Nitrogen requirement 0.045 kg N/kg glucose 3 0.109 kg NH 3 /kg PHA (4.03 MJ/kg) (0.033 NH3/glucose) Biological Processing 1 (Blanch & Clark, 1996) 2 (Akiyama et al., 2003) 3 (Lynd & Wang, in press)
Comparison of energy consumption values: ItemGeneral dataPHA fermentation (Gerngross, 1999) Sterilization steam50%*batch: 100-200 kg steam/m 3 broth 1 68 kg steam/m 3 broth Aeration900 MJe/m 3 for 50 hr 1 690 MJe/m 3 broth Agitation180-504MJe/m 3 for 50hr 1 170 MJe/m 3 broth Cooling410 MJe/m 3 broth Nitrogen requirement 440 MJ/m 3 broth 2 600 MJ/m 3 broth 1 According to data from Blanch & Clark, 1996 2 According to data from Lynd & Wang, in press
Energy uses in anaerobic fermentation: ItemEnergy use Sterilization0.29 kg steam /kg EtOH No aeration- Agitation0.75 MJe/ kg EtOH Cooling is about 1/5 of aerobic processes (less heat is released) 1 0.36 MJe / kg EtOH Nitrogen requirement is about 1/5 of aerobic processes 1 0.53 MJ / kg EtOH 1( Lynd and Wang, in press) Calculation based on values for PHA, converted using 46 wt% yield for EtOH:
Total fermentation energy use: Total energy use is related to broth volume and to fermentation time: (1) where E = energy use in absolute terms [GJ], V R = volume of reactor vessel [m 3 ] and = residence time [hr] Specific energy use (per mass of product): (2) where e = specific energy use per mass of product [GJ/kg] = mass flow of product [kg/hr] and A is a constant [GJ/(m 3 *hr)] r p = productivity [kg/m 3 /h], c = concentration of product in broth [kg/m 3 ]
Yield and productivities 1 : Maximum product yield is 90% of stoichiometric yield, with the remaining 10% being needed for growth and maintenance of the organisms Maximum productivity for anaerobic fermentation: 50-100 g/l/h Maximum productivity for aerobic process: 20 g/l/h Productivities reported for ethanol fermentation 2 : Simple, conventional batch process, usually: 1.8-2.5 g/l/h Simple CSTR up to: 6 g/l/h Continuous with cell recycle has achieved: 30-51 g/l/h Flocculating cells (internal recycle), continuous up to: 50 g/l/h Fermentation vessel coupled to membrane filtration up to: 100 g/l/h 1 These values were arrived at in a discussion with T. Nisbet and P. Nossin. 2 Ullman’s Encyclopedia
Yields of bioprocess and separation: StageCurrent yields Future yields Bio- conversion * 50%90% Separation90-95%95-98% Total45-48%86-88% * Relative to stoichiometric yield These values were arrived at in a discussion with T. Nisbet and P. Nossin.
Separations: 1. Separation of insolubles: –Filtration –Centrifugation –Decantation –Sedimentation (Depending on the type of organism) 2. Primary isolation of product (separation of water): –Extraction * –Adsorption * –Precipitation –Membrane filtration * –Distillation *
For intracellular products additional separation steps are needed: After removal of insolubles, the product stream is the insoluble fraction. This undergoes: 1. Cell disruption 2. Removal of insoluble cell debris
Separation Separation is a complex, multistep process, the details of which depend on the particular physico-chemical properties of the product Separation is easier as Boiling point of the product decreases Aqueous solubility of the product decreases Parameters giving an indication of the amount of energy needed for separation: Concentration of product in broth Heat of evaporation of product
Waste treatment Microbial biomass and unconverted feedstock (primarily lignin) can be treated by: Incineration with power generation Anaerobic digestion with power generation from the produced gases and from incineration of solids Acc. to literature: For lignocellulosic feedstocks this can supply more energy than the consumption in the plant.
Cost-determining parameters: Feedstock costs: About 2/3 of product value for mature commodity products Costs for inoculum Reactor costs: depend on the reactor size and lifetime Downstream processing costs (Utilities) In standard chemical plants the investment costs are usually 25% for reaction, 75% for product recovery. In biotechnology the ratio is currently closer to 50/50 (Nossin/Nisbet). For competitive bulk chemicals the cost price needs to be at most $900/t